A broadcast service having high definition (HD) resolution such as 1280×1024, 1920×1080, etc., has been expanded in the country and around the world. Therefore, users require contents having higher resolution and better quality of image such as 4K (3840×2160), 8K (7680×4320), or the like, so as to watch a more realistic image.
The number of pixels of a 4K image is four times larger than that of an HD image, and the number of pixels of an 8K (7680×4320) is sixteen times larger than that of the HD image. Therefore, the 4K and 8K images can be displayed delicately and naturally, as compared with the image having the HD resolution. Generally, in order to encode the 4K or 8K image, H.264/AVC (MPEG-4 Part 10 Advanced Video Coding) has been used. As such, as the resolution of an image is increased, inter-pixel spatial correlation may be largely increased.
FIG. 1 is a diagram showing comparison results of the number of pixel used to display a portion of the image, on the basis of each resolution.
In FIG. 1, when the number of pixels used to display a portion of an image is four in 480×270 resolution above QVGA (352×288) resolution, the number of pixels used to display a portion of an image is nine and twenty five, respectively, in FULL HDTV (1920×1980). Further, a portion of an image is displayed by 100 pixels in the 4K (3840×2160) resolution, and a portion of an image is displayed by 361 pixels in the 8K (7680×4320) resolution. As such, in the image of the 4K and 8K resolution, the number of pixels used to display a portion of a specific image is excessively large. In other words, the image of the 4K and 8K resolution has inter-pixel correlation much higher than that of the image of the HD resolution or less. In particular, the inter-pixel correlation is higher in an image having flat characteristics rather than having complicated characteristics or a portion of the image.
As such, when performing the intra prediction in an ultrahigh definition resolution image having the very high inter-pixel correlation such as 4K, 8K, or the like, pixel values of current blocks may be almost predicted by using only pixel values of peripheral blocks. Therefore, when the inter-pixel correlation is high, a process of encoding and decoding residual blocks is a factor of the increase in calculation complexity and the reduction in encoding efficiency.
Therefore, when encoding and decoding the ultrahigh definition resolution image having the inter-pixel correlation, a need exists for an encoding and decoding technology capable of improving the encoding efficiency while reducing the calculation complexity.